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| Two mutations on two chromosomes |
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| genes residing on the same chromosome pair. |
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| If both recessive mutations are on the same member of a chromosome pair |
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| If the dominant and recessive alleles are on opposite members of a pair |
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| Two genes that are linked |
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| Facts about Recombination |
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+ results in a the exchange of the dominant and recessive alleles of the two genes
1. the frequency of recombination between two genes is a function of the physical distance between them
2. Recombination as measured by markers is reciprocal, ie both products of exchange occur with equal frequency.
3. Recombinatino occurs at prophase 1 of meiosis when the homologues are synapsed together
4. any one combination occurs between 2 and 4 chromatids one each from a homologue but never between sister chromatids
5. two of four chromatids will be recombinant and two will be parental
5. recombination occurs at different places in different meiocytes. |
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| statistical calculation of the probability that the deviations from excpeted values can be due to chance. What is the probability that the deviation is due to chance? A high probability is good for the hypothesis for the expected ration, whereas a low probability that values are due to chance is bad for the hypothesis. |
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Number of classes-1
describe the number of values in the final calculation of a statistic that are free to vary.
Ex: there are four coat hooks on the wall. The first three people that come in have a freedom of choice, but the last one has only one hook to use. Therefore the degrees of freedom can be calculated : 4-1=3 |
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pg. 41
if we were to reject "lack of linkage" in a Chi-square test, then we would accept "linkage" and could calculate the AB/ab test cross _______________ |
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| occur between two genes, they will not appear as far apart as they actually are. One could decide the order by determining B-C. However, this will only work if the genes are far apart. |
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if double crossovers occured independently m it should be possible to predict the frequency of d.c.o.
pg 43 |
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| crossover inhibit each other from occurring nearby |
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| coefficient of coincidence |
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| f2 frequencies of linked genes |
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Definition
| one can calculate the frequencies of linked genes in an f2, by first calculating the frequency of gametes in the f1. there will be the two parental types and the two recombinant types. the map distance can be used to work backwards to determine the gametic frequencies. the gametic frequencies of the parental classes will each be 1-map distance divided by 2. the gametic frequencies of the recombinant classes will each be the map distance divided by 2. a punnett square can be produced using each gametic type and using the product rule to establish the zygotic genotype frequencies in the F2. Just as before there are two ways to get a heterozygote: dominant from maternal parent, recessive from paternal as well as recessive from maternal and dominant from paternal. |
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| normal bacteria can make cellular components on minimal media. Mutants lack the ability to synthesize some compounds, but will grow if compound is supplied. |
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| bacteria that can grow on minimal media with salts and glucose |
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| mutant that lacks the ability to make one or more nutrients |
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| naked DNA taken up by cell and recombined . |
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| unidirectional transfer of DNA via direct cell= cell contact. |
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| transfer of DNA via bacterial viruses (bacteriophage) |
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| DNA si isolated and broken into small pieces. Donor DNA is taken up by recipient strain carrying recessive markers. A double crossover is required for DNA to be incorporated into recipient chromosome. |
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| is a measure of distance between genes. If p and q are cotransformed, q and o are contransformed but p and o are not, then the order must be p-q-o. |
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first found in E. Coli
* requires the presence of F factor: F+ strains have the factor; F- do not. The F factor is a plasmid I.E a circular piece of DNA separate from the main circular DNA. It contains ~ 100 genes. The genes function in (1) F factor DNA replication; 2. produce pili for cell capture; 3. transfer of DNA to the recipient and 4 occasional recombination of F into host bacterial chromosome. |
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| transer genetc markers to F- strains at 1000 times great than F+, but F+ almost never transferred, unlike F strains. These strains have F+ integrated into host chromosome. During transfer, part of the F factor leads the way to the new cell. The remaining portion of the F factor is the last piece of DNA to transfer but the chromosome usually breaks before this happens. |
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| Allow different bacterial strains to mate for different times and then place bacteria in a Waring blender. Bacteria are then plated on agar. Hfr bacteria selected against=-killed and F- will grow and are examined for transfer of markers. As time continues more markers transferred; therefor map measured in minutes. It takes about 100 minutes for the whole E. Coli chromosome to be transferred. Different HFr strains have different staring points- because F factor is integrated at different places. It can insert in different orientations which produces transfer in opposite directions. The map produced is circular indicating the chromosome is circular. |
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Figure 5.14 & 5.15
Hfr's can excise from the chromosome and take a chunk with it that will exist as a plasmid. IF the F mates with an F-, the transconjugants will carry the normal gene on the chromosome and another copy on the F factor. This configuration is called a merodiploid. |
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| show a distribution of phenotypes |
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| show a distribution of phenotypes. The assortment of many genes with dominant/recessive or additive effects makes a distribution of phenotypes. Most quantitative traits do in fact show additive effects. |
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(A + B)^n= a^2 + 2ab + b^2
n= number of additive alleles. in this case , a and b will both equal 1 because they represent the equal contributions of two alleles for each gene involved. |
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of the number of genes involved by determining the fraction of the F2 that overlaps the parentals on both sides of the cruve.
1 gene = 1/4
2 genes = 1/16 (1/4)^2
3 genes = 1/64 (1/4)^3
4 genes = 1/256 (1/4)4 |
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| this occurs when the two parents are homozygous for different sets of alleles affecting the characteristics. they produce heterozygotes that are intermediate. |
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| the phenomenon that progeny can be outside the range of the two parents for a particular trait. |
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the statistics of mean and variance (standard diviation) are useful in analyzing polygenic traits.
1. if the variance increases from f1 to f2, multiple genes are involved because mnay genotypes are produced that cause multiple phenotypes, which causes the variation to increase
2. the magnitude of increase give an indication of how many genes |
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sum of sample measurements/n
n = number in sample |
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| = sum of squared differences of individual measure from mean/ n-1 |
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| square root of the variance |
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| populations with greater variation respond to BEEP rapidly, if the variation is cumulative |
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| environmental versus genetic component. Established by comparing variance from environment vs. genetic. Used in twin studies: monozygotic/dizygotic. Both reared apart so can partition variation into genetic and environmental components since monozygotic twins are genetically identical. Actually very difficult to do, but used in psychology for behavioral traits. |
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| the shared genes in a population are referred to as BEEP |
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| frequencies of all genotypes at a given locus in a population |
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Definition
frequency of all alleles at a locus. To calculate genotype frequency divide the three classes AA, Aa, aa by the total number in sample
AA= 90=.9
Aa=9=.09
aa=1=.01 |
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| number of copies of an allele/total number |
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Definition
1. a test of assumptions about a population
2. allows calculation of genotypic frequencies from allele frequencies (and vice versa)
for this relationship to hold the following must be true:
1. organisms are diploid
2. reproduction is sexual
3. large population
4. random mating
5. no evolutionary forces; no mutation; no migration; no natural selection
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| for x linked genes p= frequency of A in males and q = frequency of a in males. In females, p^2+2pq+ q^2=1. Thus in males, the genotype frequency equals the allele frequency, but this is not the case in females. |
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measures natural selection
+the relative reproductive ability of a genotype. |
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| selection coefficient (s) = 1-w |
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Definition
| this is a measure of the relative intensity of selection against a genotype. |
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| mean fitness of the populatoin |
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| the sum of contribution is called BEEP |
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| selective advantage of heterozygotes |
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Definition
sickle cell anemia allelic frequency goes up to .20 despite detrimental effects. it involves a change in hemoglbin. Heterozygotes have resistance to malaria. the non-affected homozygotes are susceptible to malaria and thus have reduced fitness.
effects of selection on allele frequencies (depending on the type of selection)
1. eliminate variation
2. maintain variation
3. change allele freq.
4. maintain allele freq.
5. create divergence between populations of a species
6. maintain iniformity |
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| the source of all new genetic variation is BEEp |
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| mutations that are selected against |
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| no selective advantage or disadvantage |
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| change in allele frequency due to chance. It is most dramatic in small populations. For example, if there are 10 fruit flies on a banana peel - 5 red eyed and 5 white and I come along and step on the peel killing 7- leaving 1 white and 2 red, the allele frequency has changed dramatically in the population |
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| it is homozygous in all individuals. This can occur in a small population by genetic drift. |
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| a reduction in numbers in the population changed the gene frequency. When the population size recovers, the gene frequency will be that of the small population. A genetic bottleneck refers to the situation in which a population is reduced in size and then expands again. This is usually accompanied by a change in allele frequency and sometimes in a reduction in genetic variability. |
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| the founding individuals have a different gene frequency than the population from which they came. As the new population expands, it has the allele frequency of the founders rather than the original population. This situation creates a new population with a new gene frequency. |
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Definition
| when organisms migrate and contribute to the BEEp |
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if migration continues, the allele frequencies between populations become BEEP
+increases the effective population sz and has the opposite effect of drift |
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will change genotypic frequencies without changing allele frequency in the absence of random selection.
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| Positive Assortive Mating |
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Definition
| This is the situation in which individuals with similar phenotypes mate preferentially. Humans do to some degree, e.g. tall mate with tall- short with short |
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| Negative Assortive Mating |
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| phenotypically dissimilar individuals mate more often than at random. In fruit flies, an unusual phenotypic male will be selected by females more often than random. This is called the rare male advantage. |
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Definition
| this is the situation in which mating among relatives increases homozygosity at the expense of heterozygosity. |
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| Mating between non-related individuals. |
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| mating systems maintain detrimental mutations as heterozygotes, but if no mate is available in a small population, there will be no progeny. |
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